Primulas are members of the Primulacae family of flowering ornamentals that include primrose, cowslip, oxlip and auricular. They produce colorful red, pink, purple or yellow flowers in the springtime; they are a garden favorite, and can be grown indoors in pots.
Primula seeds germinate slowly. Seeds sown immediately after harvest germinate the quickest.
Herb Dickson of the American Primrose Society recommends filling a 4-inch pot three-quarters full of a sterile seeding mix. Stir in 1 tsp. of balanced fertilizer; fill the remainder of the pot. Press the mix ¼ to ½ inch from the top; scatter the seeds on the surface. Moisten with water containing a fungicide, cover and let sit in the full sun.
Seedlings and Soil
After seedlings develop several true leaves, transplant them into your garden. Space them 4 to 6 inches apart.
Primulas like rich, well drained soil. If the soil is sandy, you can add compost so that it holds water. It may be necessary to amend heavy, clay soil with peat moss so that it drains well. Primulas grow poorly if they have to compete with roots of other plants. They grow well planted in the shade of shrubs or fruit trees.
If you are growing primulas indoors, choose a cool, bright room. Reduce the level of light during the summer. Avoid heated, dark rooms.
Watering and Fertilizing
Water primulas frequently when they are flowering. At other times of the year, let the plants begin to dry out before you water them. Do not fertilize primulas with inorganic fertilizer. Manure fertilizers and fish meal work well.
Separate clumps of primulas into individual crowns every other year. Do this immediately after they bloom but if you do this in hot, dry weather, make sure you keep them well watered. If you can protect plants during the winter by covering them with evergreen branches, it is safer to divide them in the fall. You can divide them in the spring, but that will postpone blooming.
Disease and Insects
You can avoid root and crown rot if you plant primulas in soil that drains well and you do not cover it with a heavy mulch. Miticides, insecticides that kill mites can be used on the red spider, a common pest.
Slugs are another problem with primulas. Trap slugs by sinking plastic cups every 4 to 5 feet around your garden. Fill these cups half-full of beer. Slugs and snails will tumble into the cups. Since they can't climb the plastic, they will drown.